Self-lubricating polymer bearings and bushes manufacturer Vesconite Bearings – a division of VescoPlastics – has supplied specialised thermoplastic Vesconite bushings for a tyre test rig at the University of Pretoria’s (UP’s) Vehicle Dynamics Group (VDG).
The test rig, manufactured and assembled as part of a master’s degree project by UP students, will accumulate data to develop and/or validate the various tyre models used in vehicle simulation software, says UP master’s student Kraig Wright.
Vesconite Bearings sales representative Phillip de Villiers says VDG first approached Vesconite Bearings on March 30. Thereafter VDG ordered two stock Vesconite bushings, the first measuring 110 mm (outer diameter) 50 mm (inside diameter) 1 000 mm (length). The second bushing measured 375 mm 300 mm 210 mm. VDG then machined the bushings to suit its requirements.
Wright explains that the bushings were turned down and bored out on a lathe, as the standard stock sizes did not comply with the dimensions required by the rig, but “f
ortunately, Vesconite is an easily machined material”. The bushings were installed on May 12. Wright notes that the rig assembly was completed on May 18.
Owing to the static nature of the application, Wright says it is expected that the bushes will not need to be replaced. De Villiers adds that as the bushes allow the shaft to pass through the housing without any contact, there is no metal-to-metal wear, which reduces the need for maintenance. However, he affirms that Vesconite Bearings can offer guidance on repairs and maintenance if required.
“VDG decided to commit to acquiring the bushes from Vesco because of its excellent service, specifically the quick supply of quotations and the quick delivery of the product. In terms of service in the heavy engineering industry, they are head and shoulders above everyone I have dealt with,” comments Wright.
The tyre test rig consists of a shaft pushed axially through the bushes by an actuator, and a metal plate that is pushed against a tyre during testing. Wright notes that the scale and rigidity of the rig allows for the testing of tyres with a 100 t maximum vertical load. “This broadens the rig’s range to some of the largest tyres in the world.”
He says the test rig comprises two 100 t hydraulic actuators and two 100 t load cells to measure the force applied by each actuator. The two laser displacement transducers measure the displacement against and along the tyre, while the two servo-hydraulic controllers manufactured by dynamic testing products supplier Zwick International control the servo valves on each actuator.
A hydraulic winch rotates the rig for the longitudinal and lateral tests, the wheel load cell measures the forces and moments acting on the tyre and the Helios Daq data acquisition unit captures all test data.
The rig is used to determine the vertical, lateral and longitudinal static stiffness of a tyre. Vertical stiffness is determined by loading a tyre in a vertical direction using a horizontal hydraulic actuator, while longitudinal stiffness is determined by a second hydraulic actuator that pulls the surface plate in the rolling direction of the tyre.
Thereafter, the assembly is rotated 90° to determine the tyre’s lateral stiffness, which can be acquired by pulling the surface plate away from the horizontal plane of the tyre. The various stiffness measurements are calculated by measuring the load applied to the tyre, compared with the displacement of the surface plate.
UP junior research officer Wietsche Penny says the three-dimensional computer-aided design system Solidworks was used to draw and model the test rig, the computer-aided manufacturing (CAM) process was facilitated by CAM software Autodesk HSMWorks and the data analytic programme MATLAB will be used to interpret the data gathered from the tests.
Penny adds that, at present, the test rig is used only for research purposes; however, several clients have shown interest to have large tyres tested and modelled by the rig, presenting commercial opportunities.
De Villiers says the bushes’ high-wear, self-lubricating characteristics have resulted in their having been successfully installed in the marine, rail, hydropower and pumps industries.
“It is also used in unique applications, including the tyre test rig at UP, because engineers are aware of the benefits of its properties,” he comments.
VescoPlastics chairperson Dr Jean-Patrick Leger adds that the automotive sector is an enthusiastic adopter of Vesconite products. He points out that the four-wheel-drive sector is known to use products for vehicle suspension bushes and to replace other worn parts. Additionally, owners and restorers of older, classic or vintage automobiles are a growing market for the company.
“These owners may be responding to recessionary pressures, deciding to invest in repairs that enable long-term use or they’re restorers and/or investors intent on ensuring their car retains or increases its functionality over time,” Leger notes.
Vesconite allows recession-aware users to invest in repairs to ensure that their cars are in good running order, while vintage car owners and restorers use Vesconite bushings in the absence of original parts.